This study examined factors influencing the advancement of California sage scrub (CSS) into annual grasslands. Transects were placed across boundaries between CSS and grassland, and plant species and soil samples were collected along each transect. Certain native shrub species including Artemesia californica, Eriogonum fasciculatum, Baccharis pilularis, Mimulus auirantaicus, Nassella pulchra and Melica imperfecta were disproportionately found in recovering boundaries, indicating they may be pioneer species aiding the expansion of CSS into grasslands. The results support the theory that grasses invaded CSS habitats and contradict the idea that frequent disturbances prevent CSS recovery.